Integrate `leanSpec` spec test vectors for `tests/consensus/devnet/fork choice` for testing the Lean Client

[shariqnaiyer]

Describe the feature

leanEthereum/leanSpec#76

The above PR in leanSpec outlines the test vectors that we will use to test the Lean Consensus components of our client.

As the PR is in draft, it's a good time to start planning out their integration.

This issue focuses on tests from
https://github.com/leanEthereum/leanSpec/tree/main/tests/consensus/devnet

Additional context

No response

[zemse]

it looks like the fork choice tests were completed in pr 919. is there any remaining for this issue?